That's why the former Hillsborough County commissioner and Tampa City Council member felt blindsided, even angry, in February, when she was diagnosed with Stage 3 breast cancer.

"I had been going religiously to have mammograms," said Platt, 73. "Because my younger sister died of breast cancer when she was 32, I was always very alert to it."

Platt, like most women, thought of breast cancer as a lump or an abnormal mass that can be felt. Indeed, that's the kind of cancer found in most of the roughly 192,000 American women diagnosed annually with invasive breast cancer.

But each year, 20,000 women develop invasive lobular carcinoma, a type of the disease which, in its early stages, doesn't show up on a mammogram and doesn't feel like a lump.

It starts in the milk-producing glands of the breast and breaks through the gland walls to spread to other tissue. When more advanced, it produces symptoms most women may not recognize or associate with cancer, like thickening, swelling or dimpling of the breast, a change in the texture of the breast skin or an inverted or retracting nipple.

"Invasive lobular carcinoma is about 10 to 15 percent of the breast cancers that we treat," said Dr. Nazanin Khakpour, a breast surgical oncologist at the H. Lee Moffitt Cancer Center, who is not one of Platt's physicians.

Platt says she didn't notice a skin change, just that one breast seemed smaller than the other. She went to her doctor, who ordered several tests, including a breast MRI and a biopsy.

She was shocked to learn it was breast cancer that already had spread to 12 lymph nodes under her left arm.

Khakpour says most invasive lobular carcinoma is treatable and overall the prognosis for most patients is good. Still, there is a risk of recurrence, usually within two years after diagnosis. Having it in one breast puts women at high risk for cancer in the other breast.

That's why doctors treat it aggressively with surgery, chemotherapy and radiation. And they strongly recommend that women continue with regular mammograms and breast self examination — looking not only for lumps, but any change at all.

"That way you will know if you have a change in the breast. You can detect something new or different," said Khakpour.

She also says women who are on hormone replacement therapy should be on the lowest possible dose for the briefest time because long-term hormone use — more than five years — is associated with increased risk of invasive lobular carcinoma.

In March, Platt had a mastectomy, and the affected nodes were removed. She spent the summer undergoing chemotherapy.

"They told me at the doctor's office that I would lose my hair on about the 17th day of chemo and, lo and behold, it happened right on schedule," she said. She bought a wig, wore it once and instead opted to cover her head with a buff, a tube shaped length of stretch knit fabric sold in bait and tackle stores for sun protection. She has about a dozen of them in her wardrobe.

Platt now gets radiation treatments five days a week at St. Joseph's Hospital, and also has kept up with volunteering, serving on boards and chores like grocery shopping. She looks forward to getting back to her favorite sport, fishing.

"I have to pace myself. Radiation makes you tired," she said. But cancer has made Platt determined to save other women from being blindsided as she was. "There are cancers that mammograms don't detect,'' she said.

"Keep an eye out. If you notice changes, seek other screening. Not all cancers have lumps."

Irene Maher can be reached at imaher@sptimes.comor (813) 226-3416.

Risk factors for developing invasive lobular carcinoma (ILC)

Gender: Being female is the single most significant risk factor for any type of breast cancer.